feat: add POS register screen with full-screen touch-optimized layout

Standalone register at /pos bypassing the admin sidebar layout:
- Two-panel layout: product search/grid (60%) + cart/payment (40%)
- Product search with barcode scan support (UPC lookup on Enter)
- Custom item entry dialog for ad-hoc items
- Cart with line items, tax, totals, and remove-item support
- Payment dialogs: cash (quick amounts + change calc), card, check
- Drawer open/close with balance reconciliation and over/short
- Auto-creates pending transaction on first item added
- POS link added to admin sidebar nav (module-gated)
- Zustand store for POS session state, React Query for server data

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/admin/src/components/pos/pos-drawer-dialog.tsx

@@ -0,0 +1,139 @@
+import { useState } from 'react'
+import { useMutation, useQueryClient } from '@tanstack/react-query'
+import { usePOSStore } from '@/stores/pos.store'
+import { posMutations, posKeys, type DrawerSession } from '@/api/pos'
+import { Dialog, DialogContent, DialogHeader, DialogTitle } from '@/components/ui/dialog'
+import { Button } from '@/components/ui/button'
+import { Input } from '@/components/ui/input'
+import { Label } from '@/components/ui/label'
+import { Separator } from '@/components/ui/separator'
+import { toast } from 'sonner'
+
+interface POSDrawerDialogProps {
+  open: boolean
+  onOpenChange: (open: boolean) => void
+  drawer: DrawerSession | null
+}
+
+export function POSDrawerDialog({ open, onOpenChange, drawer }: POSDrawerDialogProps) {
+  const queryClient = useQueryClient()
+  const { locationId, setDrawerSession } = usePOSStore()
+  const isOpen = drawer?.status === 'open'
+
+  const [openingBalance, setOpeningBalance] = useState('200')
+  const [closingBalance, setClosingBalance] = useState('')
+  const [notes, setNotes] = useState('')
+
+  const openMutation = useMutation({
+    mutationFn: () =>
+      posMutations.openDrawer({
+        locationId: locationId ?? undefined,
+        openingBalance: parseFloat(openingBalance) || 0,
+      }),
+    onSuccess: (session) => {
+      setDrawerSession(session.id)
+      queryClient.invalidateQueries({ queryKey: posKeys.drawer(locationId ?? '') })
+      toast.success('Drawer opened')
+      onOpenChange(false)
+    },
+    onError: (err) => toast.error(err.message),
+  })
+
+  const closeMutation = useMutation({
+    mutationFn: () =>
+      posMutations.closeDrawer(drawer!.id, {
+        closingBalance: parseFloat(closingBalance) || 0,
+        notes: notes || undefined,
+      }),
+    onSuccess: (session) => {
+      setDrawerSession(null)
+      queryClient.invalidateQueries({ queryKey: posKeys.drawer(locationId ?? '') })
+      const overShort = parseFloat(session.overShort ?? '0')
+      if (Math.abs(overShort) < 0.01) {
+        toast.success('Drawer closed - balanced')
+      } else {
+        toast.warning(`Drawer closed - ${overShort > 0 ? 'over' : 'short'} $${Math.abs(overShort).toFixed(2)}`)
+      }
+      onOpenChange(false)
+    },
+    onError: (err) => toast.error(err.message),
+  })
+
+  return (
+    <Dialog open={open} onOpenChange={onOpenChange}>
+      <DialogContent className="max-w-sm">
+        <DialogHeader>
+          <DialogTitle>{isOpen ? 'Close Drawer' : 'Open Drawer'}</DialogTitle>
+        </DialogHeader>
+
+        {isOpen ? (
+          <div className="space-y-4">
+            <div className="text-sm space-y-1">
+              <div className="flex justify-between">
+                <span className="text-muted-foreground">Opening Balance</span>
+                <span>${parseFloat(drawer!.openingBalance).toFixed(2)}</span>
+              </div>
+              <div className="flex justify-between">
+                <span className="text-muted-foreground">Opened</span>
+                <span>{new Date(drawer!.openedAt).toLocaleTimeString()}</span>
+              </div>
+            </div>
+            <Separator />
+            <div className="space-y-2">
+              <Label>Closing Balance *</Label>
+              <Input
+                type="number"
+                step="0.01"
+                min="0"
+                value={closingBalance}
+                onChange={(e) => setClosingBalance(e.target.value)}
+                placeholder="Count the cash in the drawer"
+                className="h-11 text-lg"
+                autoFocus
+              />
+            </div>
+            <div className="space-y-2">
+              <Label>Notes</Label>
+              <Input
+                value={notes}
+                onChange={(e) => setNotes(e.target.value)}
+                placeholder="End of shift notes"
+                className="h-11"
+              />
+            </div>
+            <Button
+              className="w-full h-12"
+              onClick={() => closeMutation.mutate()}
+              disabled={!closingBalance || closeMutation.isPending}
+            >
+              {closeMutation.isPending ? 'Closing...' : 'Close Drawer'}
+            </Button>
+          </div>
+        ) : (
+          <div className="space-y-4">
+            <div className="space-y-2">
+              <Label>Opening Balance *</Label>
+              <Input
+                type="number"
+                step="0.01"
+                min="0"
+                value={openingBalance}
+                onChange={(e) => setOpeningBalance(e.target.value)}
+                placeholder="Starting cash amount"
+                className="h-11 text-lg"
+                autoFocus
+              />
+            </div>
+            <Button
+              className="w-full h-12"
+              onClick={() => openMutation.mutate()}
+              disabled={!openingBalance || openMutation.isPending}
+            >
+              {openMutation.isPending ? 'Opening...' : 'Open Drawer'}
+            </Button>
+          </div>
+        )}
+      </DialogContent>
+    </Dialog>
+  )
+}